1. Field of the Invention
The present invention relates to catalysts for the polymerization of olefins. More particularly, the present invention is concerned with the application of a specific catalyst to the polymerization of .alpha.-olefins having three or more carbon atoms, thereby making it possible to producing highly stereoregular polymers under stable polymerization conditions and with industrial advantages.
Although the catalysts heretofore proposed for the polymerization of olefins comprising a solid catalyst component containing titanium, magnesium and a halogen as the essential ingredients and an orgaroaluminium have shown extremely high activity, yet it has been necessary to use an electron donative compound (electron donor) during polymerization, when the high stereoregularity of polymer products is desired.
However, problems with such catalysts using the electron donative compound as the third component (external donor) are that difficulties are encountered in the control of the performance of polymer products inclusive of the regulation of their molecular weight for reasons that the velocity of polymerization drops due to the reaction of the organoaluminium compound with the electron donative compound; when the polymerization temperature is elevated so as to increase the velocity of polymerization, said reaction is so accelerated that an attempt to increase the yield (or productivity) of polymers by doing so is subject to restriction, and other reasons.
Therefore, it is now desired to develop catalyst systems which overcome the aforesaid problems and make it possible to produce highly stereoregular polymers with improved catalytic yields but without using any electron donative compound as the third component (what is called "external electron donor").
2. Prior Art
Japanese Patent Laid-Open Publication No. 58(1983)-138715 discloses a process for carrying out polymerization with a catalyst system free from any external electron donor, which is composed of a solid component obtained by permitting (1) a titanium composite containing as the essential ingredients tetravalent titanium, magnesium, a halogen and an electron donor to react with (2) an organosilicon compound in the presence of an organoaluminium compound, or treating said titanium composite with an organoaluminium compound and, thereafter, permitting it to react with said organosilicon compound; and an organoaluminium compound.
However, it is found that such a proposal shows some signs of improvement in connection with the solving of the aforesaid problems, but there is still left much to be improved for reasons that: limitation is imposed upon the performance of the obtained polymer products; the catalyst deteriorates with time; restriction is placed upon the quantitative ratio of the titanium component and organoaluminium compound used at the time of polymerization; and other reasons.